Chemical vapor deposition (CVD) is a gas reaction process used in the semiconductor industry to form thin layers or films of desired materials on a substrate. High density plasma (HDP) enhanced CVD processes use a reactive chemical gas along with physical ion generation through the use of an RF generated plasma to enhance the film deposition by attraction of the positively charged plasma ions onto a negatively biased substrate surface at angles near the vertical to the surface, or at preferred angles to the surface by directional biasing of the substrate surface. In integrated circuit (IC) fabrication, the goal is to form very thin, yet uniform films onto substrates, at a high throughput. Many factors, such as the type and geometry of the power source and geometry, the gas distribution system and related exhaust, substrate heating and cooling, chamber construction, design, and symmetry, composition and temperature control of chamber surfaces, and material build up in the chamber, must be taken into consideration when evaluating a process system as well as a process which is performed by the system.
The most widely used CVD films are tungsten, silicon dioxide, silicon nitride and polysilicon, although other CVD films suitable as insulators, dielectrics, conductors, semiconductors, superconductors and magnetics are known. The system of the present invention has been found to be particularly effective in forming thin films of doped and undoped silicon dioxide.
One problem encountered in IC fabrication is the difficulty associated with establishing a uniform plasma density over the entire substrate surface during processing. As substrate sizes increase, i.e., to 300 mm, single coil assemblies suffer wall losses and the like, thereby creating inefficient coupling of power into the plasma resulting in center peaked or cusped plasma profiles. The resulting deposition of material under non-uniform plasma densities results in films which are typically center thick or edge thick, and in either instance tend to be non-uniform.
Another problem encountered in IC fabrication is uniform gas distribution over the substrate surface. Typically, a gas plenum is provided around the perimeter of a processing region and a plurality of nozzles extend radially inwardly to provide gases over the edge of the substrate surface. The gases tend to be unevenly distributed across the substrate surface, with more gas provided towards the edge of the substrate and less gas provided towards the center of the substrate. In addition, reactant gases are typically mixed in the gas injection system prior to their introduction into the chamber. In these instances, material may deposit within the gas injection system itself thereby clogging some gas injectors further heightening the gas distribution problems.
The use of a symmetric vacuum deposition system for HDP-CVD is taught in co-assigned U.S. patent application Ser. No. 08/574,839, entitled "Symmetric Chamber," filed Dec. 12, 1995, which is incorporated herein by reference. A principal advantage of this type of system is the enhancement of uniform deposition due to symmetrical gas flow across the surface of the wafer or substrate. Ease of removal of a substrate support member and placement of a clean support member in its place without undue down time for the system is also desirable in maintaining the highest quality and turnaround time for a deposition system. The deposition system of the present invention provides this advantage also. As cleaning of the substrate support member can be particularly time consuming if done in place, a removable substrate support is very advantageous in keeping the substrate processing equipment running as continuously as possible.
Still another difficulty encountered in IC fabrication is maintaining a uniform temperature across the substrate surface. As a substrate is processed, the temperature of the substrate is typically elevated. If a temperature gradient exists across the substrate surface, the deposition of the film can proceed in a non-uniform manner. Therefore, it is important to precisely control the temperature of the substrate.
Another problem encountered in IC fabrication is the formation of extraneous particle sources in the deposition chamber itself. During processing, deposition material deposits throughout the chamber on the chamber walls, the substrate support member and on the gas distribution system components. Over time, such material build up can flake off into the chamber resulting in particle contamination on the substrate which can compromise the integrity of the devices being fabricated. Thus, the chamber must be periodically cleaned. A favored method of cleaning is to introduce cleaning gases into the chamber to react with the deposited material to form a product which can be exhausted from the chamber. Typically, a cleaning gas, such as a fluorinated gas, is introduced into the chamber and a plasma is struck in the chamber. The resultant excited products react with the deposition material to form a stable product which is then exhausted from the chamber. One problem with this process is that the cleaning is typically localized in regions adjacent to the plasma In order to enhance cleaning of all exposed chamber surfaces, the time period in which the cleaning process is performed is increased, thereby decreasing throughput, or the cleaning process is performed using high temperatures and/or pressures, thereby effectively over cleaning the chamber surfaces and increasing the cost of consumables.
Therefore, there remains a need for a process system which provides more uniform conditions for forming thin CVD films on a substrate. It would be desirable if the system incorporates a symmetric chamber having a removable substrate support, a frequency matched, tunable coil assembly to provide a uniform plasma over the substrate surface, a gas injection system to independently and uniformly introduce gases over the substrate surface, and a remote plasma source to provide a highly efficient chamber cleaning process within the chamber.